More of the same

Posted by Miri Barak on April 13, 2003

"The actual exercise of physical violence substitues for the psychological relation between two minds, which is of the essence of political power, the physical relation between two bodies, one of which is strong enough to dominate the other's movements."

This is another complicated sentence and I'll be much obliged to you if you can rephrase it or explain it more clearly.
"which is of the essence ..." I have a difficulty with this "of", can you rephrase it?
does mind refers to souls, consciousness, thoughts...?
"the physical relation between two bodies..." is it a definition of the political power?